AP® Music Theory · Unit 5 · Topic 5.1
The ii6 Chord and Predominant Bass Lines
The ii6 chord is the ii triad in first inversion, with scale degree 4 in the bass, and it is the most common way to set up the dominant because that bass note leads smoothly down to scale degree 5.
The ii chord is built on scale degree 2. In root position its bass note is scale degree 2 itself, which does not connect especially well to the dominant chord that follows. Flip it to first inversion and the bass note becomes scale degree 4, the chord's third. Scale degree 4 sits right next to scale degree 5, the bass note of V. That half-step or whole-step motion in the bass, 4 down to 5 or sometimes 4 up through 5, is smooth and directional, which is exactly what a predominant chord should give you heading into the dominant.
This is also why ii6 so often replaces IV. Both chords share scale degrees 4 and 6, and both push toward V, but IV's root-position bass note, scale degree 4, already does the same job ii6's bass note does. Composers use ii6 for variety and for even smoother voice leading, since the upper voices of ii6 can resolve by step into V in more ways than IV's can. In a I, ii6, V, I progression in C major, the bass walks C, F, G, C: I in root position, ii6 with F in the bass, V, then I again, while the upper voices move mostly by step or common tone.
In minor keys, ii is diminished, and a diminished triad in root position puts a tritone between its outer voices, bass and soprano, which sounds unstable and ambiguous at a cadence. First inversion moves that tritone away from the outer voices, so ii6 is used almost exclusively in minor. This sets up the next topic: the full predominant-to-dominant circle progression, where ii6 or IV lead reliably into V before resolving to I.
Key terms
- Predominant function
- The role of chords like ii, ii6, and IV that prepare and lead into the dominant chord.
- ii6
- The ii triad in first inversion, with its third, scale degree 4, placed in the bass.
- Tritone
- An unstable interval of three whole steps, found between the root and fifth of a diminished triad.
- Outer voices
- The soprano and bass lines, whose relationship is most exposed to the listener's ear.
- Circle progression
- A chain of chords moving by descending fifths (or ascending fourths) that drives harmonic motion toward the dominant.
Watch it explained
- How it worksHow does putting scale degree 4 in the bass make ii6 behave like a smoother IV?
- Worked exampleWalk me through a I, ii6, V, I progression in C major written in four parts.
- Common mistakeWhy doesn't the diminished ii chord in minor appear in root position at a cadence?
- Going furtherWhat changes about the bass line when ii6 replaces IV in front of the dominant?
Check yourself
End of topic.